This invention relates to telecommunication systems and more particularly to digital subscriber lines and asynchronous transfer mode communication.
This application claims priority from Canadian Patent Application No. 2,455,303 that was filed on Jan. 16, 2004, and which is incorporated here by reference.
Digital subscriber line (DSL) technologies based on asynchronous transfer mode (ATM) have been widely adopted by communication service providers to deliver broadband access services to residential and business customers, as defined by ITU-T Recommendation G991.x, G992.x, G993.x, SHDSL, ADSL VDSL Transceivers. It is of great interest for service providers to provide higher data rates at low cost so that bandwidth-demanding services, e.g., broadcast video, video on-demand, and gaming, can be available to a wider customer base. Combining (bonding) multiple physical DSL lines to carry a larger effective payload is one possible solution to this problem.
As is well known, an ATM stream consists of a set of fixed-size cells (53 bytes each) that contain a header (5 bytes) carrying routing information and a body (48 bytes) carrying the data, as defined by ITU-T Recommendation I.361, “B-ISDN ATM Layer Specification”, February 1999. These cells are carried in an ATM network asynchronously, with the cells belonging to the same service being identified by their addressing information (Virtual Path and Virtual Circuit identifiers). As pointed out in Canadian Patent Application No. 2,386,453, titled “Higher Layer Bonding of Multiple Access Lines for Carrier Grade Access”, it is entirely feasible to transport an ATM stream over a set of diverse physical lines (referred to here as bonded lines) by distributing the ATM cells across the member lines at the transmitter.
Nevertheless, due to the fact that the bonded lines may have different data rates and different end-to-end delays, the cells arriving at the receiver may not be in the same sequence as they were transmitted. Therefore, a sequence number is added to the header as described in Canadian Patent Application No. 2,386,453. A principal role of this sequence identifier is to allow proper reconstruction of the ATM stream at the receiver in the presence of such differences in rate and delay. While the process of distributing the cells to the members of the bonded group and adding a sequence number is straightforward, the reconstruction of the proper sequence at the receiver using a minimal set of buffers is not.